In the present manufacture of fuel injectors for internal combustion engines, the interface between the needle and the valve seat is accomplished by spherical grinding and hardening the needle. The valve seat is shaped and then very precision grinding and hardening of the conical valve seat is performed. The result of this is typically a good needle-valve seat interface.
The disadvantages of the prior art processes are its cost both in terms of time and money. The grinding of the seat is a very expensive and time-consuming process. In mass production of fuel injectors, the conical grinding of valve seats requires very expensive machines and lots of them. A typical machine may cost in excess of five hundred thousand U.S. dollars annually. Add to this the cost of maintenance of these machines and the replacement of damaged or used components which can be in excess of fifteen thousand U.S. dollars, any cost savings which will increase production with any reduction in the required grinding time, is very much desired.
In the present invention, hardening of the needle and the valve seat is still required. But the time of the process of grinding to size is very much reduced. Thus, an advantage of the present invention is the reduction in the time required for grinding of the valve seat for millions of injectors each year.
It is another advantage of the invention to provide a valve needle-valve seat interface that use over time, "durability wear", does not result in any significant reduction of the amount of fuel flow past the valve seat for a given pulse time. In short, this advantage eliminates a "lean shift" in the dynamic flow rate of the injector.
Another advantage of the invention is the damping of the needle impact on the valve seat during operation of the fuel injector.
Another advantage of the invention is to reduce the closing spring force required by the return spring in the injector.
It is yet another advantage of the invention that by reducing the valve seat grinding time, the number of expensive grinding machines in manufacturing is reduced resulting in a savings in capital.